CakeDC Users plugin: how do I add flash message?

Hi,
I am using the (superbe) Users&Auth plugin from CakeDC: https://github.com/CakeDC/users
I seem to have everything working fine, but can not figure out how/where to add a flash message:

After login in the regular way (with name & password) I get a flash message saying

you’ve successfully logged in

(which is built in in the plugin). But when I log in with a social account (Google, Twiter, Facebook, etc) I do not get any message. I find this a bit unclear for my users, so I would like to add a flash message after a successfull social log in:

you’ve successfully logged in with your social account

but I can not figure out where/how?
Could anyone give me a push in the right direction? THX!

Have a great day,
Elbert